For some time now it has been possible for manufacturers of glass articles to form laminated articles, such as laminated tubing and laminated sheet glass wherein a continuous flow or stream of the composite glass is delivered to form such tubing or sheet as desired. U.S. Pat. Nos. 2,992,517 and 3,541,198 illustrate processes of forming continuous composite filaments, whereas U.S. Pat. No. 4,023,953 illustrates method and apparatus for continuously producing composite glass tubing. In the manufacture of both the filaments and the tubing, a continuous glass flow of the composite streams is necessary in order to form such filaments or tubing.
U.S. Pat. No. 3,582,306 sets forth method and apparatus for continuously forming a composite sheet or ribbon of molten glass directly from a plurality of flows of molten vitreous material, whereas U.S. Pat. No. 3,582,454 discloses method and apparatus for forming articles from such a continuous sheet of such composite material. In other words, molten glass is delivered to first form a continuous composite sheet of molten glass which is then subsequently formed and trimmed into various articles. U.S. Pat. No. 3,673,049 sets forth a plurality of compositions which may be utilized for forming both the composite sheet of the prior art and the composite encapsulated charge of molten glass of the present invention.
Whereas the prior art related to the formation of composite articles, such as tubing and sheet from a continuous flow of a composite glass, the present invention relates to the formation of individual articles from a discrete composite charge of molten glass having a core glass fully encapsulated within a skin glass, wherein the composite encapsulated charge of molten glass may be pressed into a laminated article having a core of one glass which is completely surrounded by a skin of a second glass. The use of stream feeding for forming individual charges of a single glass is shown in U.S. Pat. No. 3,351,449, however, the patent does not contemplate composite charges or the formation of laminated ware. Many applications exist for such pressed laminated ware which were not heretofore feasibly formable with the known technologies. For example, pressed articles may be formed with a core glass of a nondurable opal composition which is provided with a durable skin glass having a desired decoration or tinting. In a like manner, a charge having a core of an inexpensive glass could be encapsulated with a skin of photochromic glass which is pressformed into a laminated article having the core of the inexpensive glass completely surrounded by a skin of the photochromic glass. Further, by utilizing glass compositions disclosed in U.S. Pat. No. 3,673,049, the core and skin glasses may be chosen so as to provide a strengthened pressed laminated article having a compressive outer skin.
In addition to the formation of laminated tubing and sheet glass as shown in the aforementioned prior art, it has been known to combine multiple flows of molten glass so as to make variegated glasses used for the manufacture of variegated glass marbles as shown in U.S. Pat. No. 1,529,947. However, the process as shown in such patent was merely to combine two glasses of different colors, shear the depending glass into gobs and deposit the variegated glass in a mold for forming marbles. Although the patent indicates that a stream of glass of one color may be injected within the center of a flowing stream of glass of another color so as to form a solid tubular core of one color extending from the top to the bottom of the gob and surrounded on its sidewalls with glass of another color, and that the variegated glass may be formed into an article by any desired forming devices, the patent does not suggest or contemplate the formation of a discrete composite charge of molten glass having a core glass encapsulated within a skin glass, or the pressing of such composite encapsulated charge into a laminated article having a core of one glass which is completely surrounded by a skin of a second glass.
Commonly owned copending application Ser. No. 259,493 entitled "Forming Laminated Articles from a Composite Encapsulated Charge of Molten Glass" by R. R. Ambrogi sets forth the broad concept of forming laminated articles from a composite gob of molten glass having an inner core of one glass and an outer skin of a second glass. The present invention is actually an improvement upon the invention set forth in said copending application. That is, although laminated articles having a core of one glass surrounded by a skin of a second glass were successfully formed utilizing the invention set forth in said application, the skin on pressed articles had a tendency to become rather thin about outer peripheral edges thereof, particularly when pressing larger size articles. As the composite gob of molten glass was being pressed, the skin glass adjacent the top and bottom of the charge which is initially contacted by the plunger and mold during the pressing had a tendency to set up, whereas the hotter molten core glass tended to be squeezed radially outwardly into the finished article while materially thinning or breaking through the skin glass adjacent peripheral edge portions of the charge and the resulting article. The present invention sets forth a programmed gob which includes reentrant portions of the skin glass projecting within the core glass from peripheral edges of the gob, such that upon the pressing of the gob charge, sufficient skin glass is provided to compensate for the radially outward flow of the more fluid core glass during the pressing operation so that the finished article has a fairly uniform thickness of skin glass about its extent.